So to recap, you did use f/8, you did use a tripod, you did set a timer delay.
Your shutter speed was 1/50th sec. and whilst this should not really cause focus issues (you were using a tripod), see if you can shoot something at 1/500 sec. or faster.
Many of the comments above are very pertinent, - shoot a series from f/4 to f/16; shooting a high contrast target of some kind; If you can beg or borrow another lens to try it might confirm that your lenses are good or bad.
In answer to your question re the wind etc. Everything would be affected by gusts hitting the camera but some parts of the image more than others. If the camera moved around a pivot, then the outside pixels would travel further than the centre pixels. The outers would appear out of focus, the inners would appear to be soft.
A couple of days ago I lost sixty or so images because I had not fully tightened the locking knob on my tripod and did not notice the slow droop of the camera. Thus ended that session of time lapse. Make sure everything is locked down tightly. Tripod on solid ground, not gravel etc.
A friend of mine who has the same Sony as you - I don't know what lenses he has - told me it took a while before he got used to the camera coming from a Canon background. Several months down the line, he is now producing pin sharp images. (n.b. English pins are sharper than USA tacks
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So to recap, you did use f/8, you did use a tripod... (